1. Field of the Invention
The present invention relates to a developing apparatus preferably usable for an image forming apparatus such as an electrophotographic copier and an electrophotographic printer. Here, the developing apparatus can be installed in a cartridge and the cartridge is adapted to include a developing cartridge and processing cartridge which are attachable to and detachable from a main body of an image forming apparatus. The developing cartridge is a single body of the developing apparatus and configured as attachable to and detachable from the main body of the image forming apparatus and the processing cartridge is adapted to be configured by integration of a photosensitive body with at least one of the developing apparatus, an electrifying apparatus, and cleaning means and by making it attachable to and detachable from the main body of the image forming apparatus.
2. Related Background Art
Conventionally, electrophotography is adapted to use photoconductive substance, form an electric latent image on an electrophotographic photosensitive body by various methods, then develop the latent image with a developer (toner) to make a visualized image, and in a necessary occasion, transfer the image visualized by the toner to a recording medium such as paper, followed by fixing with heat and pressure to yield an image forming matter.
At present, improving an image resolution and definition are strongly required and thus, developing a thin toner layer forming method and an apparatus thereof become necessary. For this requirement, some measures have been proposed.
In addition, in the recent years, a contact one component developing method was proposed, in which development is carried out with a configuration, in which a surface layer of the photosensitive body is pressed by using a semiconductive developing roller or the developing roller, of which surface has a dielectric layer, as a developer carrying body.
Here, FIG. 14 shows an example of the image forming apparatus of the contact one component developing system. This system is the system by which development is carried out by contacting the electrophotographic photosensitive body 21 with the developing roller 25 and using a one component developer.
First, the electrophotographic photosensitive body 21 is evenly electrified by an electrifying roller 22 which is the electrifying means for forming a latent image on the photosensitive body 21 by a laser light from an exposing unit 3, which is the static latent image forming means. Subsequently, this latent image is visualized as a toner image by the developing apparatus 24. Following this step, the toner image developed is transferred to a transfer material 13 by a transfer roller 9. The transfer material 13 is carried to a fixing device 12, where heat and pressure are applied thereto to fix the toner image, and then, the transfer material is discharged to the outside of the apparatus. On the other hand, toner 28 not transferred to the transfer material 13 and remaining on the photosensitive body 21 is removed by a cleaning blade 23, which is the cleaning means, that is contained in a waste toner containing container 29.
The developing apparatus 24 has a developer container 20 containing nonmagnetic toner 28 as the one component developer, the developing roller 25 which is the developer carrying body installed in an opening part thereof, an elastic blade 27 which is a regulating member in which the free end makes contact with the developing roller 25, and an elastic roller 26 which is a developer carrying member contacted by pressure from a position upstream from the elastic blade 27 in a rotating direction of the developing roller 25, and by rotation of the elastic roller 26 in the direction of an arrow D. Toner 28 is supplied to the surface of the developing roller 25. Toner 28 is carried according to rotation of the developing roller 25, charged with an electric charge and made into a thin layer by friction between a contacting part of the elastic blade 27 and the developing roller 25. The toner 28 that has been made into a thin layer is carried by the developing roller 25 and supplied to the contact part with the photosensitive body 21 to develop the static latent image. Following this step, toner 28, which was not developed and which remained in the contact part of the photosensitive body 21 with the elastic roller 25, is removed by the elastic roller 26. On the other hand, as described above, a new toner 28 is supplied to the developing roller 25 by the elastic roller 26 to repeat the above described action.
In recent years, with a purpose to reduce high triboelectrification stability and fog, a system, for example, U.S. application Ser. No. 167,723 (filed on Oct. 7, 1998,), now U.S. Pat. No. 6,229,979, was proposed to use means to electrically electrify toner by using a toner electrifying roller as a developer charging member.
Here, FIG. 15 shows an example of the developing apparatus using the toner electrifying roller. This developing apparatus 40 is adapted to install the toner electrifying roller 32 in the above described developing apparatus.
The developing apparatus 4 has the developer container 30 containing nonmagnetic toner 34 as the one component developer, the developing roller 35 which is the developer carrying body installed in an opening part thereof, the elastic blade 33 which is a regulating member of which the free and contacts with the developing roller 35, and the elastic roller 36 which is the developer carrying member contacted by pressure from the upstream position from the elastic blade 33 in the rotating direction of the developing roller 35, and by rotation of the elastic roller 36 in the direction of the arrow D. Toner 34 is supplied to the surface of the developing roller 35. The toner electrifying roller 32 is located between the contact part of the photosensitive body drum 31, the developing roller 35, the contact part of the elastic blade 33, and the developing roller 35. The toner electrifying roller 32 contacts the developing roller 35.
Toner 34 supplied to the surface of the developing roller 34 is carried according to rotation of the developing roller 35 to be charged with the electric charge and made to the thin layer by friction in the contacting part of the elastic blade 33 with the developing roller 35. Further, electric charging by discharge of the toner electrifying roller 32 charges the toner with an electric charge. The charged toner 34 is carried by the developing roller 35 to the contact part with the photosensitive body 31 to develop the static latent image. Following the step, toner 34, which was not developed and remained in the contact part of the photosensitive body 31 with the elastic roller 35, is removed by the elastic roller 36. On the other hand, as described above, the new toner 34 is supplied to the developing roller 35 by the elastic roller 36 to repeat the above described action.
However, in the case where such toner electrifying roller 32 is used, the following problem results: the toner electrifying roller 32 contacts the developing roller 35 and hence, toner 34 attaches to the toner electrifying roller 32 to decrease an electric charging performance of the toner electrifying roller 32. Particularly, in the case where a voltage over a discharge starting voltage is applied to the toner electrifying roller 32, the voltage applied increases and therefore, toner becomes easy to attach to the electrifying roller.
An object of the present invention is to provide a developing apparatus in which a developer is prevented from attaching to a developer electrifying member.
Another object of the present invention is to provide a developing apparatus in which the developer attached to the developer electrifying member is returned to the developer carrying member.
A further object of the present invention is to provide a developing apparatus in which stability of the electric charge of the developer is kept for a long period so as to provide a good image.